1. Field of the Invention
The present invention relates to a viscous heater incorporated in a heating system for motor vehicles, etc. wherein a heat generating chamber and a heat radiating chamber are partitioned in a housing, a viscous fluid sealed in the heat generating chamber is subjected to shearing upon the rotation of a rotor to generate heat, and the generated heat is transmitted to a circulating fluid in the heat radiating chamber, thereby heating the circulating fluid.
2. Description of Related Art
As an auxiliary heat source loaded in motor vehicles, viscous heaters utilizing the driving force of an engine have received attention recently. Japanese Patent Application Laid-open No. 2-246823, for example, discloses a viscous heater incorporated in a heating system for motor vehicles.
In the disclosed viscous heater, front and rear housings are coupled together in opposite relation to each other to define therein a heat generating chamber and a water jacket (i.e., a heat exchange chamber) around the heat generating chamber. A drive shaft is rotatably supported by the front housing through a bearing unit, and a rotor is fixed to one end of the drive shaft to be rotatable with it in the heat generating chamber. Concentric recesses and projections are formed in complementary relation to mesh with each other on the front and rear outer wall surfaces of the rotor and the front and rear inner wall surfaces of the heat generating chamber. These recesses and projections are closely positioned to define labyrinthine clearances (labyrinth grooves) between the above outer and inner wall surfaces. A predetermined amount of viscous fluid (silicone oil, for example) is sealed in the heat generating chamber to fill the labyrinth grooves.
When the driving force of the engine is transmitted to the drive shaft, the rotor is rotated in the heat generating chamber together with the drive shaft, and the viscous fluid between the inner wall surfaces of the heat generating chamber and the outer wall surfaces of the rotor is subject to shearing upon the rotation of the rotor to generate heat based on fluid friction. The heat generated in the heat generating chamber is transmitted to the circulating water flowing in the water jacket, and the heated circulating water is then supplied to an external heating circuit to heat the motor vehicle.
The amount of heat generated by the above stated conventional viscous heater increases with an increase in the contact area of the viscous fluid, i.e., the total surface area of the outer wall surfaces of the rotor and the inner wall surfaces of the heat generating chamber. On the other hand, when a viscous heater is utilized as a heat source for heating motor vehicles, from the standpoint of ensuring enough space to mount other automotive accessories in the engine compartment, there is a need to make the viscous heater as small as possible. For this reason, the above conventional viscous heater increases the amount of heat generated with labyrinth grooves which are formed between the front and rear outer wall surfaces of the rotor and the front and rear inner wall surfaces of the heat generating chamber in opposite relation to enlarge the total surface area of the outer wall surfaces of the rotor and the inner wall surfaces of the heat generating chamber, i.e., to make the contact area (hereinafter referred to as the effective heat generating region) between these parts and fluid larger so as to increase the shearing force applied to the viscous liquid, while avoiding an increase in the size of the rotor and the housing.
However, the labyrinth grooves must be provided by machining the rotor and the inner wall surfaces of the heat generating chamber to form complicated recesses and projections. This manufacturing technique raises problems as it is difficult to achieve high machining accuracy of the recesses and projections and it increases the production costs. It is thus difficult to practically employ a structure with labyrinth grooves. Specifically, in the above conventional viscous heater wherein the labyrinth grooves are defined by the concentric recesses and projections formed about the axis of the rotor, the rotor may interfere with the inner wall surfaces of the housing with even a slight inclination of the drive shaft unless the recesses and projections are machined and assembled with extremely high accuracy.